ES2685655T5 - Liquid cleaning concentrate - Google Patents

Description

DESCRIPTION

Liquid cleaning concentrate

The invention relates to a liquid cleaning concentrate, which comprises at least one alkali metal hydroxide. The invention further relates to a process for the production of a liquid cleaning concentrate, which comprises alkali metal hydroxide.

State of the art

For cleaning dishes, especially for removing dirt that has adhered to dishes, alkaline cleaning agents are preferably used.

Liquid cleaning agents based on hydroxides and complexing agents are known from the state of the art and have advantages over powder formulations. On the one hand, there is no formation of fine dust and, on the other hand, handling is simplified when dosing with pumps.

Liquid cleaning concentrates containing alkali metal hydroxide are described, for example, in DE 199 06 660 A1, where a water content of 53 - 80% by weight is mentioned. However, such a high water content in liquid cleaning concentrates is disadvantageous for the stability of the concentrate and considerably increases the required volume of cleaning concentrate, which is accompanied by the need for additional containers. Particularly in the commercial sector, highly concentrated cleaning concentrates with a small volume are preferred for storage and transport as well as for reasons of environmental protection.

To counteract the disadvantageous high water content, different strategies are followed in the prior art. Non-aqueous liquid cleaning concentrates, as described in EP 1181 346, are one strategy; but such compositions are associated with reduced cleaning capacity or the handling of chemicals harmful to health or harmful to the environment.

Another approach is to reduce the water content in aqueous cleaning concentrates, which, however, leads to an increase in viscosity. For example, DE 100 02 710 A1 describes a cream-shaped cleaning concentrate with a water content of 32.5%.

WO 96/27653 A1 discloses a paste-like cleaning agent with a viscosity of more than 15,000 mPa*s which cannot flow out of a container without prior intervention by shear forces. Cleaning concentrates are industrially metered using automatic dosing devices and automatically diluted with water to the desired final concentration in the ready-to-use cleaning agent. In such automatic dosing devices, peristaltic pumps are generally used to meter the cleaning concentrate, and these peristaltic pumps can only meter liquid cleaning concentrates. Creamy or pasty cleaning concentrates are not suitable for use in automatic dosing devices due to their high viscosity (in the worst case, clogging and damage to the peristaltic pump or automatic dosing device occur).

The aim of the present invention is therefore to provide a highly concentrated, yet liquid, cleaning concentrate based on alkali metal hydroxide, which can be dosed and diluted with an automatic dispenser.

Brief description of the invention

This objective is achieved by a liquid cleaning concentrate, which comprises

(i) 22 to 46% by weight of alkali metal hydroxide,

(ii) 5 to 50% by weight of dispersing agent, complexing agent or a combination thereof,

(iii) 0 to 5% by weight of surfactant,

(iv) 0 to 5% by weight of adjuvants, and

(v) 28 to 39% by weight of water,

wherein the liquid cleaning concentrate is a suspension with a suspension viscosity of at most 6500 mPas, measured according to ISO 2555:1989 at 20°C and a rotational speed of 5 rpm.

The measurement can take place, for example, with a Brookfield viscometer.

The suspensions described in this document are stable suspensions.

Within the scope of the invention it has been discovered that the reduction in the water content and the increase in viscosity normally associated with it can be avoided when the cleaning concentrate is produced in the form of a suspension.

It is preferably provided that the cleaning concentrate does not contain any additional substances. However, the production of a stable suspension with a high concentration of alkali metal hydroxide in a small amount of water is not possible with conventional processes for producing suspensions. Stable alkali metal hydroxide suspensions cannot be produced with the known production processes for suspensions according to the prior art, and if (unstable) suspensions can be produced, they have such a high viscosity that dosing is impossible.

Therefore, the present invention has also set itself the objective of providing a process for the production of a stable suspension.

The objective is achieved by a process for the production of a suspension, which comprises

(i) 22 to 46% by weight of alkali metal hydroxide,

(ii) 5 to 50% by weight of dispersing agent, complexing agent or a combination thereof,

(iii) 0 to 5% by weight of surfactant,

(iv) 0 to 5% by weight of adjuvants and

(v) 28 to 39% by weight of water, the process comprising the steps of:

a) providing a portion of dispersing agent, complexing agent or a combination thereof in aqueous phase,

b) if necessary, add adjuvants,

c) in the case of adding adjuvants, then add an additional portion of dispersing agent, d) add a portion of alkali metal hydroxide as an aqueous solution,

e) if necessary add a surfactant,

f) add an additional portion of alkali metal hydroxide,

g) add a dispersing agent,

h) add an additional portion of alkali metal hydroxide,

the addition steps taking place with stirring and at least addition steps d) to h) taking place in such a way that a temperature of at most 40°C, preferably at most 35°C, is maintained in the aqueous phase.

In this respect, “adding a portion” means that only a part and not the entire amount of the respective substance contained in the respective stage is added.

This process makes it possible to produce a stable suspension (i.e. a suspension which does not separate during storage or use and in which no precipitates or solids are deposited). This makes it possible for the first time to produce a stable suspension containing large amounts of alkali metal hydroxide and (in contrast to the cream-like composition according to DE 100 02 710 A1) a liquid cleaning concentrate which can be pumped and metered.

Terms:

For the purposes of this invention, the terms mentioned in the application are understood as follows: a cleaning agent represents a ready-to-use preparation for cleaning and is a mixture of a cleaning concentrate with water. Preferably, the cleaning agent is a ready-to-use preparation for cleaning dishes.

A cleaning concentrate is a composition in which the substances contained (with the exception of the diluent water) are present in highly concentrated form, as a ready-to-use cleaning product.

A stable suspension is herein understood to mean a suspension which does not separate and in which no precipitates form during storage and use. Stability can be measured, for example, by measuring the viscosity and density, which may vary only insignificantly over time. Stability can also be determined by a climate change test or storage over a defined period of time and subsequent optical monitoring (separation into two or more phases). One measurement option is to check whether the viscosity and density change after 30 days of storage, i.e. without agitation or movement of the suspension, at 20°C by sedimentation by less than 5%.

Alkali metal hydroxide is understood to mean hydroxides of at least one alkali metal. It can therefore also be a mixture of several alkali metal hydroxides. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are preferably used.

A dispersing agent is an additive that improves the optimal mixing of at least two immiscible substances. In this respect, dispersing agents also aim at an improved cleaning performance of the cleaning agent. A dispersing agent can also be understood as a mixture of two or more dispersing agents. In this respect, a dispersing agent in the cleaning agent also helps to break down old deposits.

A complexing agent or chelating agent is an additive which forms chelating complexes with metal ions. In this way, undesirable properties of certain metal ions are masked. In particular, divalent metal ions, especially alkaline earth metal ions such as Ca2+ and Mg2+, are not desired in the cleaning operation. Complexing agents are therefore preferably those which form complexes with alkaline earth metal ions.

However, in cleaning products, some complexing agents also act as dispersing agents and vice versa.

Surfactants are substances that reduce the surface tension of a liquid or the interfacial tension between two phases and thus support the formation of dispersions. They can also act as solubilizers. There may also be a mixture of two or more surfactants.

In cleaning agents, they are intended to promote the transfer of grease and dirt particles adhering to dishes into the aqueous phase. These can be selected, for example, from the group of alkylbenzene sulphates, alkyl polyglycosides, esterquats, fatty alcohol ethoxylates, fatty alcohol sulphates and fatty alcohol ether sulphates or mixtures thereof, with fatty alcohol ethoxylates showing particularly good cleaning performances.

Adjuvants comprise compounds which can facilitate the use of the finished cleaning agent or enhance its cleaning action. However, adjuvants can also comprise compounds which promote the formation of a suspension. Typical adjuvants are, for example:

• defoaming agents, i.e. substances that reduce the formation of unwanted foam when the cleaning product is shaken,

• thickening agents, which increase the viscosity of the cleaning product,

• cleaning enhancers, which enhance the cleaning action of alkaline metal hydroxides,

• barrier substances,

• suspending agents or else also

• aromatic substances,

to mention just a few examples.

Defoaming agents can be selected, for example, from the group of paraffin oils, silicone oils or mixtures thereof. An example of a possible paraffin oil is white, technical oil (Bussetti); an example of silicone oil is silicone oil 100 (Bussetti). The defoaming agent content can be, for example, from 0 to 5% by weight.

Thickening agents can be selected, for example, from the group of 1,2,3-propanetriol, propan-2-ol, xanthan gum (e.g. Keltrol types, CP Kelco). The thickening agent content can be, for example, from 0 to 5% by weight.

Cleaning enhancers can be, for example, substances that have a basic action, i.e. they act by increasing the pH value, and can be, for example, monoethanolamine or triethanolamine. Other cleaning enhancers include polymers or alkaline compounds, such as Mirapol SURF S (a mixture based on Na<2>CO<3>; Rhodia), Polyquart Ampho 149 (BASF). The content of cleaning enhancers can be, for example, from 0 to 5% by weight.

The suspending agents may be selected, for example, from the group consisting of polyvinyl alcohol or polyvinylpyrrolidone. The suspending agent content may be, for example, 0 to 2% by weight. Preferably, no suspending agent is provided, since it has been shown that segregation and sediment formation occur with increasing amounts of suspending agents.

Barrier substances are compounds which, at very low (substoichiometric) concentrations, prevent the formation of precipitates or at least delay it considerably. In a supersaturated solution, the formation of an insoluble precipitate is prevented by the barrier substances blocking the surface of the microcrystals that are formed first by adsorption, so that larger crystals cannot form by deposition. In the cleaning industry, for example, compounds from the group of low-molecular-weight phosphonates and high-molecular-weight complexing agents (e.g. polycarboxylates) are known as barrier substances.

A particularly suitable barrier substance was Hydrodis WP 40, which contains an oligomeric phosphonic acid as the main component. Although it is known that many barrier substances have solubility problems in aqueous solutions with high calcium concentrations (so-called calcium sensitivity), no Ca-sensitive zones were observed when oligomeric phosphonic acid was added in the form of Hydrodis WP 40. The addition of Hydrodis WP 40 ensures that the cleaning concentrate remains stable and has a very good calcium binding capacity as well as a good cleaning performance. The barrier substance content is preferably 2 to 5% by weight.

Detailed description of the invention

Further advantages and details of the invention will be explained below. The embodiments relate to the liquid cleaning concentrate and the production process for the suspension at the same time. However, for the sake of better understanding, the production process is set forth first.

Step a) Providing a portion of dispersing agent, complexing agent or a combination thereof in aqueous solution:

First, a solution of dispersing agent, complexing agent or a combination thereof in water is provided.

Preferably a mixture of a first and a second complexing agent is provided.

A first complexing agent may be selected, for example, from the group of aminocarboxylic acids and a second complexing agent from the group of aminophosphonic acids.

In a variant embodiment, in step a) a mixture of an aqueous solution of the first complexing agent (such as an aminocarboxylic acid, even more preferably methylglycinediacetic acid or a salt thereof) and an aqueous solution of a second complexing agent (such as an aminophosphonic acid, even more preferably diethylenetriaminopentamethylenephosphonic acid or a salt thereof) can be provided.

Step b) Add adjuvants if necessary:

In step b) adjuvants may be added.

Step c) Add an additional portion of dispersing agent:

If adjuvants are added, it is advantageous to add an additional portion of dispersing agent at a later stage. The addition of adjuvants and the subsequent addition of dispersing agent lead to a more stable suspension.

Step d) Add a portion of alkali metal hydroxide as an aqueous solution:

In step d), a first addition of alkali metal hydroxide, in particular as an aqueous solution, takes place with stirring. With respect to the total amount of alkali metal hydroxide, preferably less than half, particularly preferably less than one third of the final amount of alkali metal hydroxide is added in this step.

Aqueous solutions that may preferably be considered are those of NaOH or KOH, it does not make any difference whether a NaOH solution or a KOH solution is used or whether a NaOH solution and a KOH solution are added separately in each case or whether a NaOH/KOH mixture is added. All combinations of these are also possible.

Step e) Add a surfactant:

In step e) a surfactant is added with stirring.

Step f) Add an additional portion of alkali metal hydroxide:

In step f) a further portion of alkali metal hydroxide is added as a solid. Preferably, the addition takes place by stirring in granules of NaOH and/or KOH.

Step g) Add an additional portion of dispersing agent:

In step g) an additional portion of dispersing agent is added, which is incorporated with stirring. Step h) Add an additional portion of alkali metal hydroxide:

In step h), the remaining amount of alkali metal hydroxide is slowly added with stirring, at least part, preferably the entire remaining amount of alkali metal hydroxide being added as a solid. Preferably, the addition takes place by introducing NaOH and/or KOH granules with stirring.

Temperature of maximum 40°C, preferably maximum 35°C for addition steps d) to h):

From step d) onwards, the aqueous phase can no longer reach a temperature above 40°C. The inventors have found that steps d) to h) must be carried out at temperatures in the range of 15°C to a maximum of 40°C in order to achieve a stable suspension with the above-mentioned properties. In the temperature range from 15 to 35°C, no influence of temperature on the stability and viscosity of the suspension was observed. With increasing temperatures, the solubility of NaOH and/or KOH increases increasingly. However, if the temperatures during addition were above 40°C, a stable, meterable suspension could no longer be achieved, since the cleaning concentrate would have a pasty consistency after cooling.

Furthermore, it was found that the suspension produced according to the invention, when heated to temperatures above 60°C, thickened irreversibly after cooling, which is attributable to the disadvantageous alteration of the suspension.

Temperature control can be achieved, for example, by cooling (e.g. with a cooling sleeve) or by appropriately slow process control. In step d), it is helpful, for example, to add a finished alkali metal hydroxide solution so that no significant temperature increase occurs.

Preferably, active external cooling is provided (e.g. cooling sleeve).

For the production of the suspension, an agitator, for example an anchor agitator, may be provided.

In a variant embodiment, a dispersant is additionally provided to accelerate the formation of the suspension.

A surprising insight of the inventors was that for two reasons it is advantageous to add at least partly KOH as alkali metal hydroxide to the composition. Basically, the person skilled in the art gives priority to NaOH for different reasons compared to KOH: KOH is more expensive compared to NaOH. Furthermore, the cleaning performance of a pure KOH solution for dishwashing is (slightly) worse than the cleaning performance of a pure NaOH solution. Furthermore, KOH is known to react more intensively with CO<2> in the air than NaOH and to form carbonates in the solution (“scale formation”). Finally, pure KOH exhibits a stronger exotherm during the dissolution operation (enthalpy of dissolution - 57.1 kJ/mol) compared to NaOH (enthalpy of dissolution - 44.5 kJ/mol), which would basically discourage the person skilled in the art from using KOH, if he has to maintain a low temperature in the aqueous phase.

However, within the scope of the present invention, the inventors have found that the absorption of CO<2> when adding KOH leads to a lower scale formation than when using NaOH alone. Scale formation is not desired, since the suspension is transported via a suction lance to the pump and scale can clog the suction lance. The presence of KOH is therefore preferred. Despite a substantially higher exotherm when dissolving KOH, it was shown that when adding KOH granules in step f), the spontaneous temperature rise was lower than when adding NaOH granules, so that the process can be controlled more easily.

As for the composition of the liquid cleaning concentrate, which is a suspension, the following could also be discovered:

i) 22 to 46% by weight of alkali metal hydroxide:

Dishwashing detergents show the best cleaning performance at high concentrations of alkali metal hydroxides. For the present invention, an addition of up to 46% by weight of alkali metal hydroxide was possible, with which a stable suspension could be achieved, the viscosity of which was within the range mentioned above. For the reasons mentioned above, NaOH (22 to 46% by weight), KOH (22 to 46% by weight) or mixtures thereof (NaOH: 25 to 46% by weight - x% by weight; KOH: x% by weight) are preferred.

The highest suspension stability was achieved with a mixture of NaOH and KOH, in which the KOH content was between 5 and 10% by weight.

ii) 5 to 50% by weight of dispersing agent, complexing agent or a combination thereof:

A particularly good cleaning action of the cleaning agent is achieved when at least one dispersing agent and at least one complexing agent are present in the cleaning concentrate. Particularly preferably, the dispersing agent comprises a polymeric dispersing agent. A preferred cleaning concentrate comprises 1 to 10% by weight of polymeric dispersing agent.

In a preferred embodiment, it has proven to be advantageous if the complexing agent has an organic amino function, preferably selected from the group comprising aminocarboxylic acids, aminophosphonic acids or a combination thereof. In this way, a liquid cleaning concentrate could be produced in a particularly advantageous manner.

It turned out to be advantageous if the polymeric dispersing agent is a polycarboxylic acid, preferably polyacrylic acid or a derivative thereof.

iii) 0 to 5% by weight of surfactant:

The proportion of surfactants must not be too high due to foaming behaviour and stability, as well as for cost and environmental reasons. Preferably up to 2% by weight, particularly preferably 0.5 to 1.5% by weight, is used. Surfactants known per se for dishwashing can be used. However, in one variant embodiment it has proven to be advantageous if the surfactant is a nonionic surfactant, preferably a fatty alcohol alkoxylate or a derivative thereof. Fatty alcohol alkoxylate 8 (Plurafac LF 400, BASF) has proven to be a particularly suitable surfactant.

iv) 0 to 5% by weight of adjuvants:

As regards the adjuvants, reference may be made to the previous embodiments. Preferably, between 1 and 3% by weight of adjuvant is added. In this respect, monoethanolamine is particularly preferably added. v) 28 to 39% by weight of water:

The water content is preferably 28 to 39% by weight, with concentrations below 28% by weight not having the desired viscosities. Although concentrations above 39% by weight can be produced as a suspension, the advantage over a solution is not as great in this case. In one variant embodiment, it is provided that the liquid cleaning concentrate is free of ethanol, glycerol and other short-chain alcohols (C<1> to C<5> alcohols), since it has been shown that such alcohols increase the viscosity, i.e. act as thickeners. It has also been shown that incorporation of NaOH solutions in alcohols, polyols or glycerol with the addition of solid NaOH leads to uncontrolled hardening and inhomogeneous thickening.

In a preferred embodiment, the cleaning concentrate does not have any components other than those mentioned above.

Experimental results and example of implementation:

The liquid cleaning concentrate described above is a stable suspension and has a viscosity such that it can be pumped into a dosing system and dosed with it. It is therefore provided that the viscosity of the liquid cleaning concentrate is at most 6500 mPas, measured according to ISO 2555:1989 at 20°C and a rotational speed of 5 rpm.

Examples

Formulations and production processes for cleaning concentrates according to the invention are shown below as examples, as well as their rheological properties, and are compared with comparative examples not according to the invention.

E m l 1: E m l n l inv n i n

The total water content is 36.5% by weight. During the production process, cooling took place so that the maximum temperature of 35°C was not exceeded. The viscosity of the suspension was:

Viscosity (mPas): 4500 mPas, measured based on ISO 2555:1989 at 20°C and 5 rpm

The total water content is 37.4% by weight. During the production process, cooling took place so that the maximum temperature of 35°C was not exceeded. The viscosity of the suspension was:

Viscosity (mPas) 6000 mPas, measured based on ISO 2555:1989 at 20°C and 5 rpm

The total water content is 37.4% by weight. During the production process, cooling took place so that the maximum temperature of 35°C was not exceeded. The viscosity of the suspension was:

Viscosity (mPas) 3800 mPas, 20°C measured based on ISO 2555:1989 at 20°C and 5 rpm E m l m r iv 1:

The total water content is 40.0% by weight.

During the production of the concentrate from comparative example 1, no temperature control was provided. During the production process, a maximum temperature of 75°C occurred. The concentrate was already highly viscous immediately after production; after 24 hours, the composition was gelatinous. The presence of glycerol was detrimental to viscosity stability.

E m l m r iv 2:

___ ___

Total water content: 35.4% by weight.

The preparation is free of surfactants. The formulation proved to be too viscous without temperature control during production. With temperature control in the production process (maximum temperature 35°C), the viscosity of the suspension was still in the range of 6500 mPa s. However, the complete absence of surfactants proved to be negative for the viscosity. An addition of 0.5% by weight showed a reduction in viscosity and an increase in stability.

A reduction in the water content of water-based cleaning concentrates usually leads to an increase in viscosity. DE 10002710 A1 describes a cream-like cleaning concentrate with a water content of 32.5%. However, the cream or paste properties are unfavourable for use in automatic dosing units due to the high viscosity. Such a cleaning agent could not be dosed into the dosing unit using a peristaltic pump.

A cleaning concentrate produced by the process according to the invention has two differences to the cream- or paste-like cleaning agents according to DE 100 02 710 A1: Firstly, in DE 10002710 A1 a homogeneous mixture without particles is produced, i.e. no suspension is formed. Secondly, the cleaning concentrate of DE 10002710 A1 has a considerably higher viscosity, which results in poor dosability.

In the following Table 1 a cleaning concentrate according to the invention is compared with the cleaning concentrate according to DE 10002710 A1.

Table 1: Viscosity comparison of cleaning concentrates:

Brookfield Viscometer based on ISO 2555:1989.

The individual measurement results for example 1 were:

The composition according to Example 3 was further produced under different conditions, i.e. at different temperatures. Addition steps d) to h) took place in such a way that a temperature of 40°C was not exceeded in the aqueous phase (see Table 2).

T l 2: m r i n l vi i - m i i n n l m l .

In samples 1, 3 and 4, a maximum temperature of 35°C occurred, in sample 2 a temperature of 40°C briefly occurred. The measurement values correlate with the temperature that occurred at its maximum, i.e. in sample 1 the lowest temperatures occurred, in sample 2 the highest.

Claims (9)

1. Cleaning concentrate, comprising (i) 22 to 46% by weight of alkali metal hydroxide, (ii) 5 to 50% by weight of dispersing agent, complexing agent or a combination thereof, (iii) 0 to 5% by weight of surfactant, (iv) 0 to 5% by weight of adjuvants, and (v) 28 to 39% by weight of water, wherein the liquid cleaning concentrate is a suspension with a suspension viscosity of at most 6500 mPas, measured according to ISO 2555:1989 at 20°C and a rotational speed of 5 rpm. 2. Cleaning concentrate according to claim 1, characterized in that the alkali metal hydroxide is sodium hydroxide, potassium hydroxide or a mixture thereof. 3. Cleaning concentrate according to claim 2, characterized by - 20 to 41% by weight of sodium hydroxide and - 5 to 10% by weight of potassium hydroxide. 4. Cleaning concentrate according to one of claims 1 to 3, characterized in that the dispersing agent comprises at least one complexing agent and a polymeric dispersing agent. 5. Liquid cleaning concentrate according to claim 4, characterized by - 5 to 49% by weight of complexing agent and - 1 to 10% by weight of polymeric dispersing agent. 6. Liquid cleaning concentrate according to claim 4 or 5, characterized in that the complexing agent has an organic amino function, preferably selected from the group comprising aminocarboxylic acids, aminophosphonic acids or combinations thereof. 7. Liquid cleaning concentrate according to one of claims 3 to 7, characterized in that the polymeric dispersing agent is a polycarboxylic acid, preferably polyacrylic acid or a derivative thereof. 8. Liquid cleaning concentrate according to one of claims 1 to 7, characterized in that the adjuvant is monoethanolamine. 9. Procedure for the production of a suspension, comprising i) 22 to 46% by weight of alkali metal hydroxide, (ii) 5 to 50% by weight of dispersing agent, complexing agent or a combination thereof, (iii) 0 to 5% by weight of surfactant, (iv) 0 to 5% by weight of adjuvants and (v) 28 to 39% by weight of water, the procedure comprising the steps of: a) providing a portion of dispersing agent, complexing agent or a combination thereof in aqueous solution, b) if necessary, add adjuvants, c) in the case of adding adjuvants, then add an additional portion of dispersing agent, d) add a portion of alkali metal hydroxide as an aqueous solution, e) if necessary add a surfactant, f) add a portion of alkali metal hydroxide as a solid, g) add a dispersing agent, h) add an additional portion of alkali metal hydroxide, the addition steps taking place with stirring and at least addition steps d) to h) taking place in such a way that a temperature of at most 40°C, preferably at most 35°C, is maintained in the aqueous phase.